Re: [Libguestfs] [PATCH v2 1/4] file: Avoid unsupported fallocate() calls

When using file systems not supporting ZERO_RANGE (e.g. NFS 4.2) or block device on kernel < 4.9, we used to call fallocate() for every zero, fail with EOPNOTSUPP, and fallback to manual zeroing. When trimming, we used to try unsupported fallocate() on every call. Change file handle to remember if punching holes or zeroing range are supported, and avoid unsupported calls. - zero changed to: 1. If we can punch hole and may trim, try PUNCH_HOLE 2. If we can zero range, try ZERO_RANGE 3. Fall back to manual writing - trim changed to: 1. If we can punch hole, try PUNCH_HOLE 2. Succeed --- plugins/file/file.c | 80 ++++++++++++++++++++++++++++++--------------- 1 file changed, 53 insertions(+), 27 deletions(-)

#ifdef FALLOC_FL_ZERO_RANGE - r = do_fallocate (h->fd, FALLOC_FL_ZERO_RANGE, offset, count); - if (r == -1 && errno != EOPNOTSUPP) { - nbdkit_error ("zero: %m"); + if (h->can_zero_range) { + r = do_fallocate (h->fd, FALLOC_FL_ZERO_RANGE, offset, count); + if (r== 0)